The electronics of motor vehicles are usually supplied with the aid of a vehicle battery which provides a DC voltage of 12 V, 24 V or 48 V. The supply lines from electrical loads are generally protected using fuses close to the battery. A distinction can be made between two types: switched supply lines and non-switched supply lines. The switched supply lines are disconnected, for example using a switch between the fuse and the supply line, when the vehicle is parked. Non-switched supply lines are always connected to the battery via a fuse.
There is a potential safety problem, especially in the case of loads with a non-switched voltage supply. This safety problem lies in the fact that, in an electronic control unit (ECU), various fault mechanisms may result in an uncontrolled current flow in the control unit, but without tripping the fuse. Such an uncontrolled current flow may consequently cause a severe temperature increase which, in the extreme case, may result in a fire in the control unit and even in a fire in the vehicle.
Due to the concept, the uncontrolled current flow cannot be disconnected in a non-switched supply even if the fault were detected by electronics. The disconnection function could fundamentally be performed with an upstream fuse. However, if the uncontrolled current flow is not large enough to trip the fuse, the uncontrolled current flow may result in damage despite the presence of the fuse.